Observation and Spectral Measurements of the Crab Nebula with Milagro

Abstract

The Crab Nebula was detected with the Milagro experiment at a statistical significance of 17 standard deviations over the lifetime of the experiment. The experiment was sensitive to approximately 100 GeV - 100 TeV gamma ray air showers by observing the particle footprint reaching the ground. The fraction of detectors recording signals from photons at the ground is a suitable proxy for the energy of the primary particle and has been used to measure the photon energy spectrum of the Crab Nebula between ~1 and ~100 TeV. The TeV emission is believed to be caused by inverse-Compton up-scattering scattering of ambient photons by an energetic electron population. The location of a TeV steepening or cutoff in the energy spectrum reveals important details about the underlying electron population. We describe the experiment and the technique for distinguishing gamma-ray events from the much more-abundant hadronic events. We describe the calculation of the significance of the excess from the Crab and how the energy spectrum is fit. The fit is consistent with values measured by IACTs between 1 and 20 TeV. Fixing the spectral index to values that have been measured below 1 TeV by IACT experiments (2.4 to 2.6), the fit to the Milagro data suggests that Crab exhibits a spectral steepening or cutoff between about 20 to 40 TeV.

Submitted to Astrophysical Journal

References in corpus (10)

• Observations of the Crab Nebula with H.E.S.S
• Fermi Large Area Telescope Bright Gamma-ray Source List
• Gamma-ray flares from the Crab Nebula
• Discovery of Powerful Gamma-Ray Flares from the Crab Nebula
• Milagro Observations of Multi-TeV Emission from Galactic Sources in the Fermi Bright Source List
• Discovery of TeV Gamma-Ray Emission from the Cygnus Region of the Galaxy
• Observation of Pulsed Gamma-rays Above 25 GeV from the Crab Pulsar with MAGIC
• Discovery of Localized Regions of Excess 10-TeV Cosmic Rays
• Long-term monitoring of the TeV emission from Mrk 421 with the ARGO-YBJ experiment
• On the variability of the GeV and multi-TeV gamma-ray emission from the Crab Nebula

Cited by in corpus (24)

• Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory
• Sensitivity of the High Altitude Water Cherenkov Detector to Sources of Multi-TeV Gamma Rays
• First Detection of Photons with Energy Beyond 100 TeV from an Astrophysical Source
• Dark Matter Limits From Dwarf Spheroidal Galaxies with The HAWC Gamma-Ray Observatory
• Identification of the TeV Gamma-ray Source ARGO J2031+4157 with the Cygnus Cocoon
• Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes
• Crab Nebula: five-year observation with ARGO-YBJ
• First HAWC Observations of the Sun Constrain Steady TeV Gamma-Ray Emission
• The Study of TeV Variability and Duty Cycle of Mrk 421 from 3 Years of Observations with the Milagro Observatory
• Novel Gamma-Ray Signatures of PeV-Scale Dark Matter
• Characteristics of extensive air showers around the energy threshold for ground-particle-based gamma-ray observatories
• Search for Dark Matter Gamma-ray Emission from the Andromeda Galaxy with the High-Altitude Water Cherenkov Observatory
• High energy gamma-ray emission from compact galactic sources in the context of observations with the next generation Cherenkov Telescope Arrays
• High-Time-Resolution Measurements of the Polarization of the Crab Pulsar at 1.38 GHz
• Reconcilement of VHE $\gamma$-ray/X-ray correlation studies in Mrk 421 and break-down at high fluxes
• Prospects for the characterization of the VHE emission from the Crab Nebula and Pulsar with the Cherenkov Telescope Array
• Milagro Observations of Potential TeV Emitters
• Analysis Methods for Gamma-ray Astronomy
• A comparative study on different background estimation methods for extensive air shower arrays
• Validation of standardized data formats and tools for ground-level particle-based gamma-ray observatories
• Energy calibration of LHAASO-KM2A using the cosmic ray Moon shadow
• Expected performance of the ALTO particle detector array designed for 200 GeV - 50 TeV gamma-ray astronomy